1. Field of the Invention
This invention relates to the field of aerospace, and in particular to the deployment of small satellites in low-earth orbit (LEO).
2. Description of Related Art
Satellites, because of their unobstructed fields of view of large areas of the earth, are often the preferred technical solutions to a variety of communications and monitoring problems. The high cost of satellite deployment, however, often precludes their use from a cost-efficiency viewpoint. In order to distribute the high costs of deployment among a large number of applications or users, the majority of deployed satellites are those that handle a multitude of tasks, or a multitude of customers for the same task. To minimize the loss of available access time to or from the satellite from or to the location on earth being serviced by a satellite, many satellites are placed in geosynchronous orbit. A geosynchronous orbit tracks the revolution of the earth, so that the satellite appears to be fixed over the same area of the earth, thus providing continual access to that area. Due to the physics involved, a geosynchronous orbit is approximately 36,000 kilometers above the earth. To provide reliable communications over this long distance, a geosynchronous satellite requires highly sensitive receivers and/or highly powerful transmitters. Because of the aforementioned economic and technical requirements, geosynchronous satellites generally weigh a ton or more, and cost (in 1999) hundreds of millions of dollars to deploy to the selected geosynchronous orbit.
As contrast to large geosynchronous satellites, the use of small satellites at low-earth orbit (LEO) are becoming increasingly common. Copending U.S. patent applications "SATELLITE COMMUNICATION SYSTEM WITH A SWEEPING HIGH-GAIN ANTENNA", U.S. Ser. No. 09/045,971, filed Mar. 21, 1998 for Fleeter et al, Attorney docket AA980217; "LOW-COST SATELLITE COMMUNICATION SYSTEM", U.S. Ser. No. 09/045,970, filed Mar. 21, 1998 for Fleeter et al, Attorney docket AA980218; "IN SITU REMOTE SENSING", U.S. Ser. No. 09/130,854, filed Aug. 7, 1998 for Richard Fleeter, Attorney docket AA980723; "RF INSPECTION SATELLITE", U.S. Ser. No. 09/267,942, filed Mar. 11, 1999 for Hanson et al, Attorney docket AA990202 illustrate the use of low cost satellites for a variety of applications, and are incorporated by reference herein. Low-earth orbits are typically hundreds of miles above the earth, rather than thousands of miles. Because of their order of magnitude closer proximity to earth, satellites in low-earth orbit require significantly less communicating and monitoring power and sensitivity than the satellites in geosynchronous orbit. Because they are not stationary above any location on the earth, multiple satellites in low-earth orbit are required to provide continuous coverage of a particular area on earth. Because multiple satellites are required in low-earth orbit to provide continuous coverage, a low-earth orbit satellite system is particularly well suited to applications that employ low cost satellites. As advances continue to be made in electronic circuit density and efficiency, the number of communication and monitoring applications that can be embodied in small, low cost satellites continues to increase.
Deployment of a small, less than five hundred pound, satellite into low-earth orbit typically costs, in 1999 dollars, between seven and ten million dollars. Because a plurality of satellites is required to provide continuous coverage of an area, the overall cost of deploying constellations of low-earth orbit satellites can often amount to hundreds of millions of dollars.